The 20-year-old third baseman had been trying to rehabilitate a strained ulnar collateral ligament in his right elbow. He was hurt in October while playing winter ball in his native Dominican Republic.

Twins doctors, along with orthopedic surgeon Dr. James Andrews, recommended rest for Sano in early November.

Despite making strides during a two-month throwing program, Sano reported pain in his elbow after making an off-balance throw during an intrasquad game Thursday.

An MRI exam revealed a partially torn ligament.

''When I threw a couple days ago, (there was) no injury, no pain, nothing. When I threw to first, it hurt a little and I talked to the trainer,'' Sano said. ''I think when I come back I will be the same player.''

The Twins said the surgery will likely take place in March.

''We wanted to give him an opportunity to try and rehab it,'' Twins assistant general manager Rob Antony said. ''If it would have worked, he wouldn't have missed the season. It didn't work.''

The recovery period for position players is shorter than it is for pitchers undergoing Tommy John surgery.

The Twins expect Sano to resume hitting in about four months, and he should return to playing the field in eight months.

Sano hit a combined 35 home runs last season between Class A Fort Myers and Double-A New Britain while batting .280 with 103 RBIs and counts Boston slugger David Ortiz among his mentors. Sano hit 28 homers with 100 RBIs in 2012 at Class A.